Limit google-api-client batch deletes to ~100.

Suggestion made by @Capstan 

We should change [`DefaultStorageRpc`](https://github.com/GoogleCloudPlatform/gcloud-java/blob/master/gcloud-java-storage/src/main/java/com/google/gcloud/spi/DefaultStorageRpc.java) and potentially invoke multiple sequential batch requests to avoid sending more than 100 delete requests per google-api-client batch.
